This week's chemical element is mercury, which has the atomic number 80 and the symbol Hg. Its symbol comes from its former name, hydrargyrum (Greek for "water silver"), and it is commonly known as quicksilver.

Mercury is remarkable because it is the only metal that is liquid at room temperature. It is a dense, lustrous grey metal. Mercury is extremely rare in the Earth's crust and in the wild, it typically is concentrated near volcanically active areas, either as the pure metal or in a number of minerals.

Although widely used in the past in batteries, fluorescent lighting, thermometers, mirrors, reconstructive dentistry, medicines and cosmetics, mercury is currently used mostly by the chemical industry and in research. The reason mercury was so popular is because it readily forms stable amalgams with a number of other metals, particularly silver and gold, making them workable at lower temperatures, and these amalgams have been the source of many instances of mercury poisoning. One notable mercury poisoning event resulted from the application of 100 pounds of a gold amalgam to the dome of St Isaac's cathedral in St Petersburg, Russia, which claimed the loves of 60 workmen.

Biologists are quite interested in mercury because it is highly toxic to life, causing both acute and chronic poisoning. Mercury can be absorbed through the skin and mucous membranes and mercury vapors can be inhaled. Mercury is concentrated in the body over the lifetime of the individual, and it also becomes more concentrated when one animal eats another, which is how it moves up the food chain. This is the reason why the flesh of tuna, a long-lived apex predator in the oceans, contain such high levels of mercury.

Historically, mercury was used as a de-wormer, for tanning animal skins, and felt hats were from a highly toxic solution of matted animal fur and liquid mercury. Those who made felt hats inhaled the fumes and often suffered from mercury poisoning, which inspired the phrase "mad as a hatter".

In this video, two of our favourite chemistry professors tell us a little bit about the wonders of mercury:

Ancient alchemists thought fluidity was an essential and unique property of mercury, so they were shocked when two Russians demonstrated in 1759 that mercury could be frozen into a solid and bent like any other metal.

In this next video, the professor introduces us to a University College London chemist, Professor Andrea Sella, who shows us a bell that he created from solid mercury -- something that would have shocked early alchemists: